Coating stack comprising a layer of barrier coating

ABSTRACT

A coating composition that contains at least one degradable coating layer and at least one layer of barrier coating is disclosed. The coating composition can be used to make a coated substrate having improved performance over conventional coated substrates after exposure to heat and certain chemicals like halides such as chlorides, sulfur, salt, chlorine, alkali, and enamels.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No. 10/816,519filed Apr. 1, 2004, which was a continuation-in-part of U.S. applicationSer. No. 10/422,095 filed Apr. 24, 2003, which was acontinuation-in-part of U.S. application Ser. No. 10/397,001 filed Mar.25, 2003, and claims the benefit of U.S. Provisional Application Ser.No. 60/376,000 filed Apr. 25, 2002. U.S. application Ser. No. 10/422,095which was also a continuation-in-part of U.S. application Ser. No.10/133,805 filed Apr. 25, 2002, which was a continuation-in-part of U.S.application Ser. No. 10/007,382 filed Oct. 22, 2001. All of theseapplications are herein incorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates generally to multi-layer functionalcoatings; especially such coatings that contain at least one layer ofbarrier coating.

BACKGROUND OF THE INVENTION

Substrates such as glass are used in a multitude of applications rangingfrom commercial buildings, homes, automobiles, appliances, etc. Thesubstrates are often coated with functional coatings to obtain thedesired performance attributes.

A wide variety of functional coatings are known in the art including,but not limited to, electroconductive coatings, solar control coatings,photocatalytic coatings, low emissivity coatings, transparent conductivecoatings, etc. An example of a functional coating is a metallic basedhigh transmittance, low emissivity coating that includes at least onemetallic layer(s) sandwiched between layers of dielectric material.Usually, the metallic layer is gold, copper, or silver, and thedielectric material is a metal oxide such as tin oxide, indium oxide,titanium oxide, bismuth oxide, zinc oxide, zirconium oxide or zinc/tinoxide.

For certain applications, it is necessary to heat a substrate coatedwith a functional coating. For example, a coated glass substrate thatwill be used as an automotive windshield may need to be heated to bendthe glass. Typically, glass will be heated for 20-30 minutes to amaximum temperature of 1150° F. to 1200° F. to accomplish the necessarybending for an automotive windshield. Depending on the complexity of thebend, the temperatures could be higher and the duration longer.

Heating a coated substrate can be problematic if the coating contains alayer(s) that will degrade upon heating. Generally, heating a coatedsubstrate will produce beneficial results up to a certain temperature(for a certain duration of time) for various reasons, for example,mobile species becoming mobile upon heating and flowing out of certaincoating layers, but then adverse affects arise. The combination oftemperature and exposure time to which a coating layer can be heatedbefore the performance of the coating starts to degrade is referred toherein as the “heat budget” of the coating. The performance of a coatingstarts to degrade after its heat budget is exceeded because at least onelayer of coating will start to degrade. Every coating layer in a coatingstack has a different heat budget that depends on the materials used tomake the coating. The heat budget for a coating stack is determined bythe layer of coating in the stack with the lowest heat budget at whichthe layer starts to degrade.

For example, in the high transmission, low emissivity coating asdescribed above, the metallic layer(s) typically has the lowest heatbudget in the coating stack. When a glass substrate coated with such acoating is exposed to heating conditions typically associated withbending, e.g. 1150° F. to 1200° F. for a period of 20 to 30 minutes, themetallic layer(s) will degrade. The degradation of the metallic layer(s)can result in a coated substrate with reduced optical and/or solarcontrol properties. Specifically, the functional coating can demonstrateincreased electrical resistivity, increased haze, decreased solarinfrared (IR) reflectance, decreased visible light transmittance,increased emissivity, etc.

In addition to heating, other things can cause degradation of layers ina functional coating, such as exposure to certain chemicals including,but not limited to halides such as salt, chlorides, sulfur, chlorine,alkali, and enamels.

To ensure optimal performance of a coated substrate, it is desirable toprotect any degradable coating layer(s) in a coating stack fromconditions and/or substances that would result in degradation of thecoating layer and subsequent decreased performance of the coatedsubstrate. Conventionally, sacrificial layers like primer layers (alsoknown as “blocker layers”) have been added to coating stacks, such asmetallic based high transmission, low emissivity coatings, or applied atthicker levels to protect a degradable layer(s). The sacrificial layerspreferentially respond to or react with the undesirable condition so asto protect other selected layers in the coating stack. The problem withadding a primer layer(s) or using a thicker layer(s) of primer is thatafter the coating is heated, excess primer can lead to poor adhesion dueto failure at the interfaces of individual layers of coating andincreased haze. Also, excess primer can make the coating soft andsusceptible to damage by rubbing.

The present invention provides a coating composition having at least onelayer of barrier coating to protect any degradable layer(s) in thecoating stack. Coating compositions according to the present inventionexhibit an increased heat budget and improved ability to withstandchemical corrosion.

SUMMARY OF THE INVENTION

In one non-limiting embodiment, the present invention is a coatingcomposition comprising at least one degradable layer and at least onelayer of barrier coating, wherein the layer of barrier coating has apermeability to oxygen no greater than 10 grams per m² per day at atemperature of 900° F.

In another non-limiting embodiment, the present invention is a coatedsubstrate comprising a coating composition applied on at least a portionof the substrate comprising at least one degradable layer and at leastone layer of barrier coating, wherein the layer of barrier coating has apermeability to oxygen no greater than 10 grams per m² per day at atemperature of 900° F.

In yet another non-limiting embodiment, the present invention is amethod of forming a multilayered coated substrate comprising applying adegradable coating layer on a substrate and applying a layer of barriercoating on the degradable coating layer, wherein the barrier coatinglayer has a permeability of to oxygen of no greater than 10 grams per m²per day at a temperature of 900° F.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a heat study conducted on several coated substratesincorporating features of the present invention.

DESCRIPTION OF THE INVENTION

As used herein, spatial or directional terms, such as “left”, “right”,“inner”, “outer”, “above”, “below”, “top”, “bottom”, and the like, areunderstood to encompass various alternative orientations and,accordingly, such terms are not to be considered as limiting.

Further, as used herein, all numbers expressing dimensions, physicalcharacteristics, processing parameters, quantities of ingredients,reaction conditions, and the like, used in the specification and claimsare to be understood as being modified in all instances by the term“about”. Accordingly, unless indicated to the contrary, the numericalvalues set forth in the following specification and claims may varydepending upon the desired properties sought to be obtained by thepresent invention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical value should at least be construed in light of the numberof reported significant digits and by applying ordinary roundingtechniques. Moreover, all ranges disclosed herein are to be understoodto encompass the beginning and ending range values and any and allsubranges subsumed therein. For example, a stated range of “1 to 10”should be considered to include any and all subranges between (andinclusive of) the minimum value of 1 and the maximum value of 10; thatis, all subranges beginning with a minimum value of 1 or more and endingwith a maximum value of 10 or less, e.g., 1.0 to 3.8, 6.6 to 9.7, and5.5 to 10.0.

As used herein, the terms “on”, “applied on/over”, “formed on/over”,“deposited on/over”, “overlay” and “provided on/over” mean formed,deposited, or provided on but not necessarily in contact with thesurface. For example, a coating layer “formed over” a substrate does notpreclude the presence of one or more other coating layers of the same ordifferent composition located between the formed coating layer and thesubstrate. For instance, the substrate (e.g. glass or ceramic) caninclude a conventional coating such as those known in the art forcoating substrates.

The present invention is a coating composition that comprises at leastone layer of barrier coating and at least one layer of coating that issusceptible to degradation upon exposure to certain conditions such as,but not limited to, heat and chemical attack. The layer of coating thatis susceptible to degradation is referred to herein as the “degradablelayer”.

The layer of barrier coating according to the present invention can be asingle layer or multiple layers of coating. The layer of barrier coatingcan serve as a barrier against various materials such as, but notlimited to, oxygen, copper, halides, sulfides, sulfur, alkali, water,etc. The layer of barrier coating of the present invention issubstantially stable, substantially non-consumable, and substantiallynon-reactive. By substantially stable, substantially non-consumable, andsubstantially non-reactive, it is meant that the stoichiometric ratio ofthe components in the barrier layer to O₂ will not change more than plusor minus 5%, for example during a conventional heating or bendingprocess for a conventional automotive windshield. Regardless of theconditions the layer of barrier coating is exposed to, it will remainessentially the same compositionally. For example, in the case of anoxygen barrier coating, if the layer of barrier coating starts fullyoxidized, it will remain fully oxidized regardless of the conditions.

According to the present invention, when the layer of barrier coating isprotecting the degradable layer from oxygen, the layer of barriercoating has a low permeability to oxygen. In a non-limiting embodimentof the invention, the layer of barrier coating exhibits a permeabilityto oxygen of no greater than 10 grams per m² per day at a temperature of900° F., for example, no greater than 8 grams per m² per day or nogreater than 5 grams per m² per day.

The following illustrates how permeability to oxygen can be measured.Three clear pieces of glass were coated with a 1400 Å thick first layerof barrier coating comprising an alloy of alumina and silica (60 weight% alumina and 40 weight % silica). Next, a coating comprising a 114 Ålayer of titanium was applied over the layer of alumina/silica alloy.Lastly, the samples were coated with a second layer of barrier coatingcomprising an alloy of alumina and silica (60 weight % alumina and 40weight % silica). The thickness of the second barrier layer wasdifferent for each sample. One sample (Sample A) had a second barrierlayer having a thickness of 266 Å. Another sample (Sample B) had asecond barrier layer coating having a thickness of 515 Å. The lastsample (Sample C) had a second barrier layer having a thickness of 1,071Å. Initially, all the samples appeared dark on transmission as a resultof the absorption of the titanium layers.

After the samples were prepared, each sample was heated at 1300° F. Theamount of time it took for the samples to become clear (no absorption)was recorded. When a sample becomes clear, that indicates that thetitanium that was initially deposited has fully oxidized and becometitania. Sample A took 80 minutes to fully oxidize. Sample B took 115minutes to fully oxidize. And, Sample C took 130 minutes to fullyoxidize. The recorded “oxidation” times were used to calculatepermeabilities (P) using the following equation:P=T/10E ⁸ [Å/cm]×4.5 [g/cm³]×10E4 [cm²/m²]/47.9 [g/mol]×32[g/mol]/R×1440 [min/day]

where

T=thickness of titanium layer [Å];

4.5 g/cm³=density of titanium;

47.9 g/mol=atomic weight of titanium;

32 g/mol=molecular weight of O₂; and

R=recorded oxidation time in minutes.

The permeability of Sample A was calculated to be 0.6 grams per m² perday. The permeability of Sample B was calculated to be 0.4 grams per m²per day. And, the permeability of Sample C was calculated to be 0.4grams per m² per day.

According to the present invention, the layer of barrier coating canhave an index of refraction equal to any value at 550 nm. When the layerof barrier coating is comprised of multiple layers, the index ofrefraction of the entire layer of barrier coating can be calculatedusing standard techniques which are well known in the art. In anon-limiting embodiment, the entire layer of barrier coating has anindex of refraction equal to 3 or less, for example 2.5 or less, or 1.8or less.

In a non-limiting embodiment of the invention, the layer of barriercoating is a single layer comprised of one or more metal oxide materialssuch as but not limited to, alumina, silica, or mixtures thereof. Forexample, the layer of barrier coating can be made up entirely of aluminaor entirely of silica. In another non-limiting embodiment, the layer ofbarrier coating can be a combination of alumina and silica, for example,but not limited to, 5 weight percent to 95 weight percent alumina and 95weight percent to 5 weight percent silica, or 10 weight percent to 90weight percent alumina and 90 weight percent to 10 weight percentsilica, or 15 weight percent to 90 weight percent alumina and 85 weightpercent to 10 weight percent silica, or 50 weight percent to 75 weightpercent alumina and 50 weight percent to 25 weight percent silica.

In a non-limiting embodiment of the invention, the layer of barriercoating comprises a single layer and the composition of the barriercoating varies throughout. For example, the barrier coating compositioncan be comprised of two materials; a first material and a secondmaterial. The layer of barrier coating is applied on a substrate in sucha manner that the concentration of the first material of the barriercoating is greatest near the substrate and the concentration of secondmaterial of the barrier coating increases, for example, gradually, asthe distance from the substrate increases. The composition of thebarrier coating furthest from the substrate has the greatestconcentration of the second material. In another non-limiting embodimentof the invention, the barrier coating is a single layer and thecomposition of the barrier coating is generally uniform throughout.

In a non-limiting embodiment of the invention, the thickness of thelayer of barrier coating can range up to 2 microns (20,000 Å), forexample, from 50 Å to 5,400 Å, or from 85 Å to 600 Å.

In a non-limiting embodiment of the invention where the layer of barriercoating is comprised of multiple layers, the barrier coating comprises afirst layer of silica and/or alumina and a second layer of silica and/oralumina. For example, the first layer can comprise alumina or asilica/alumina mixture having greater than 5 weight percent alumina, forexample, greater than 10 weight percent alumina, or greater than 15weight percent alumina. The first layer can have a thickness up to 1micron, for example, from 50 Å to 400 Å, or from 60 Å to 300 Å. Thesecond layer can comprise a silica/alumina mixture having greater than40 weight percent silica, for example, greater than 50 weight percentsilica, or greater than 60 weight percent silica. The second layer canhave a thickness up to 1 micron, for example, from 50 Å to 5,000 Å, orfrom 60 Å to 300 Å. Each of the layers that comprise the layer ofbarrier coating can have a uniform composition or a composition thatvaries throughout.

According to the present invention, the layer of barrier coating can beincorporated into any functional coating known in the art. In anon-limiting embodiment of the invention, the layer of barrier coatingis incorporated into a metal based coating composition. As used herein,metal based coating composition includes any coating that contains atleast one layer of metal. Specifically, the layer of barrier coating canbe incorporated into a metal based coating composition comprising one ormore layers of a unit metal based coating stack which is described indetail below. The unit metal based coating stack can be repeated anynumber of times to produce a cascade design as is well known in the art.

The unit metal based coating stack comprises a first layer of dielectricmaterial, a layer of electromagnetic radiation reflective material, alayer of primer, and a second layer of dielectric material. The firstlayer of dielectric material can be comprised of metal oxides or oxidesof metal alloys which are transparent to visible light. Non-limitingexamples of suitable metal oxides include indium oxide, titanium oxide,zinc oxide, tin oxide and mixtures and alloys thereof (e.g. zincstannate). For example, the first layer of dielectric material cancomprise an alloy of zinc and tin in proportions ranging from 10 to 90weight percent zinc, for example, from 30 to 60 weight percent zinc, orfrom 46 to 50 weight percent zinc. As another example, the first layerof dielectric material can be comprised of multiple layers, e.g., onelayer of zinc stannate and another layer of zinc oxide. A suitable firstlayer of dielectric material is described in U.S. Pat. Nos. 4,610,771and 5,821,001, which are hereby incorporated by reference.

The thickness of the first layer of dielectric material can range from100 Å to 800 Å, for example, from 200 Å to 750 Å, or from 280 Å to 700Å.

A layer of electromagnetic radiation reflective material is applied overat least a portion of the first layer of dielectric material. Theelectromagnetic radiation reflective material can reflect in the solarinfrared region, in the thermal infrared region, and/or in the microwaveregion. The electromagnetic radiation reflective material can comprise ametal such as gold, copper, or silver. The electromagnetic radiationreflective material can also comprise a combination of theaforementioned metals as well as alloys thereof. In the described unitmetal based coating stack, the layer of electromagnetic radiationreflective material is the degradable layer.

The thickness of the layer of electromagnetic radiation reflectivematerial can range from 50 Å to 300 Å, for example, from 60 Å to 200 Å,or from 70 Å to 150 Å.

A layer of primer is applied over at least a portion of the layer ofelectromagnetic radiation reflective material. The layer of primer canbe any material known in the art as a gettering/scavenging material,i.e., a material that readily absorbs a gas. Suitable materials for theprimer include, but are not limited to, titanium, copper, aluminum,nickel, niobium, yttrium, zirconium, hafnium, chromium, and alloysthereof; nickel-chromium alloy and cobalt-chromium alloy; sub-oxidessuch as indium tin sub-oxide, titanium sub-oxide, and zinc aluminum suboxide; and nitrides such as silicon nitride.

In a non-limiting embodiment of the invention, the layer of primer canconvert from a metal to an oxide or from a sub-oxide to an oxide due to,for example, exposure to an O₂ containing plasma or as a resulting ofbeing heated in air. The fact that the primer may lose its ability as agetterer/scavenger over time does not affect its classification as aprimer. For example, a coating stack according to the present inventioncan contain a layer of primer initially comprised of titanium metal.Over time, as the layer of titanium metal absorbs oxygen, the titaniummetal will convert to titania, i.e. TiO₂. Titania does not further reactwith oxygen. In such case, the titania that was initially present in thecoating stack as titanium metal is considered the layer of primer.

The thickness of the layer of primer can range up to 50 Å, for examplefrom 5 Å to 35 Å, or from 8 Å to 30 Å, or from 10 Å to 18 Å.

A second layer of dielectric material is applied over at least a portionof the layer of primer. Suitable materials for the second layer ofdielectric material and the thickness of the applied layer are asdescribed above for the first layer of dielectric material.

The layer of barrier coating can be applied anywhere within a coatingcomposition comprised of one or more the unit metal based coating stacksdescribed above. In a non-limiting embodiment of the invention, thecoating composition includes a single unit metal based coating stack anda layer of barrier coating is applied over the second layer ofdielectric material. In another non-limiting embodiment of theinvention, the coating composition includes a single unit metal basedcoating stack and a layer of barrier coating is applied over the firstlayer of dielectric material. In yet another non-limiting embodiment ofthe invention, a layer of barrier coating is applied on the substrateand a single unit metal based coating stack is applied over the layer ofbarrier coating.

In another non-limiting embodiment of the invention, at least one layerof barrier coating is incorporated anywhere in a coating compositionthat repeats the unit metal based coating stack described above at leasttwo times, e.g. three times wherein the coating stack comprises threelayers of electromagnetic radiation reflective material. In a particularembodiment, the coating composition includes three unit metal basedcoating stacks and a layer of barrier coating is the last layer ofcoating, i.e., it is applied on at least a portion of the second layerof dielectric material of the third unit metal based coating stack. Inanother specific embodiment, two layers of barrier coating are includedwith a layer of barrier coating forming the first and last layer of thecoating stack.

In various non-limiting embodiments of the invention, other coatinglayers comprised of various materials can be applied over the layer ofbarrier coating; particularly when the layer of barrier coating is thelast coating layer in a coating stack. In one non-limiting embodiment ofthe invention, a layer of titanium metal is applied over the layer ofbarrier coating. In another non-limiting embodiment, a layer of carbonis applied over the layer of barrier coating. Applying a dark, heatabsorbing layer of coating like carbon over the layer of barriercoating, can increase the heating rate of the coated substrate.

In another non-limiting embodiment of the present invention, the layerof barrier coating is incorporated into a coating stack comprising atleast the following layers: at least one layer of a transparent,conductive oxide, e.g., fluorine doped tin oxide, indium tin oxide, orzinc aluminum oxide, and at least one layer of a conductive nitride,like titanium nitride or zirconium nitride. The arrangement of the layerof a conductive nitride and layer of transparent, conductive oxide isimmaterial, i.e., the layer of conductive nitride can be applied on atleast a portion of the layer of transparent, conductive oxide and viceversa. In this embodiment, the layer of barrier coating can be the firstand/or last coating in the stack.

In the coating stack described above, the layer of conductive nitride isthe degradable layer.

The thickness of the layer of transparent, conductive oxide can rangefrom 1 Å to 5,000 Å, for example, from 5 Å to 2,500 Å. The thickness ofthe layer of conductive nitride can range from 1 Å to 2,500 Å, forexample, from 5 Å to 1,000 Å, or from 10 Å to 500 Å.

In addition to the various coating compositions, the present inventionencompasses methods for making the coatings. Specifically, the presentinvention encompasses a method of forming a multilayered coatedsubstrate comprising applying a degradable coating layer on a substrateand applying a layer of barrier coating on the degradable coating layer,wherein the barrier coating layer has a permeability to oxygen of nogreater than 10 grams per m² per day at a temperature of 900° F. Thelayer of barrier coating can be the last layer in the coating stack orit can be placed within a coating stack. In a non-limiting embodiment,the present invention further comprises applying additional coatinglayers on the degradable coating layer prior to applying the barrierlayer coating. In another non-limiting embodiment, the present inventionfurther comprises applying another layer of barrier coating on thesubstrate prior to applying the degradable coating layer.

The various layers of coating discussed above can be applied usingconventional techniques such as chemical vapor deposition (“CVD”), spraypyrolysis, and magnetron sputtered vacuum deposition (“MSVD”).

Suitable CVD methods of deposition are described in the followingreferences, which are hereby incorporated by reference: U.S. Pat. Nos.4,853,257; 4,971,843; 5,536,718; 5,464,657; 5,599,387; and 5,948,131.

Suitable spray pyrolysis methods of deposition are described in thefollowing references, which are hereby incorporated by reference: U.S.Pat. Nos. 4,719,126; 4,719,127; 4,111,150; and 3,660,061.

Suitable MSVD methods of deposition are described in the followingreferences, which are hereby incorporated by reference: U.S. Pat. Nos.4,379,040; 4,861,669; and 4,900,633. In a non-limiting embodiment of theinvention where MSVD is used to deposit the layer of barrier coating, atarget comprising 60 weight percent aluminum and 40 weight percentsilicon can be sputtered to deposit a layer of barrier coatingcomprising a mixture, alloy, or combination of alumina and silica.

The multi-layer coating composition of the present invention can beapplied on various substrates. Examples of suitable substrates include,but are not limited to, plastic substrates (such as acrylic polymers,such as polyacrylates; polyalkylmethacrylates, such aspolymethylmethacrylates, polyethylmethacrylates,polypropylmethacrylates, and the like; polyurethanes; polycarbonates;polyalkylterephthalates, such as polyethyleneterephthalate (PET),polypropyleneterephthalates, polybutyleneterephthalates, and the like;polysiloxane containing polymers; or copolymers of any monomers forpreparing these, or any mixtures thereof; metal substrates, such as butnot limited to steel, galvanized steel, stainless steel, and aluminum;ceramic substrates; tile substrates; glass substrates; or mixtures orcombinations of any of the above. For example, the substrate can beconventional untinted soda-lime-silica-glass, i.e., “clear glass”, orcan be tinted or otherwise colored glass, borosilicate glass, leadedglass, tempered, untempered, annealed, or heat-strengthened glass. Theglass can be of any type, such as conventional float glass or flatglass, and can be of any composition having any optical properties,e.g., any value of visible radiation transmission, ultraviolet radiationtransmission, infrared radiation transmission, and/or total solar energytransmission. Types of glass suitable for the practice of the inventionare described, for example but not to be considered as limiting, in U.S.Pat. Nos. 4,746,347; 4,792,536; 5,240,886; 5,385,872; and 5,393,593.

The substrate can be any thickness. In the embodiment wherein thesubstrate is glass, generally, the substrate is thicker forarchitectural applications than for automotive applications. In anon-limiting embodiment for an architectural application, the substratecan be glass having a thickness ranging from 1 mm to 20 mm, for example,1 mm to 10 mm, or 2 mm to 6 mm. In a non-limiting embodiment for anautomotive application, the substrate can be at least one glass ply in alaminated automotive windshield or sidelight, and the substrate can beup to 5.0 mm thick, for example, up to 4.0 mm, or up to 3.0 mm, or up to2.5 mm thick, or up to 2.1 mm thick.

When the substrate is glass, the glass can be manufactured usingconventional float processes, e.g., as described in U.S. Pat. Nos.3,083,551; 3,220,816; and 3,843,346 which are hereby incorporated byreference. In a non-limiting embodiment of the invention, the coatinglayers as discussed herein can be applied to the glass during the floatglass process, e.g., while the glass is being supported on molten tinwithin a float bath.

In a non-limiting embodiment, the present invention encompasses thecoated substrate described below. A first dielectric layer comprised ofzinc stannate is deposited on a substrate at a thickness from 250 Å to490 Å, for example, from 340 Å to 440 Å, or 375 Å to 425 Å. A firstsilver layer is deposited on the first dielectric layer at a thicknessfrom 50 Å to 175 Å, for example, from 60 Å to 125 Å, or from 67 Å to 90Å. A first titanium primer layer is deposited on the first silver layerat a thickness from 10 Å to 30 Å, for example, from 12 Å to 25 Å, orfrom 15 Å to 22 Å. A second zinc stannate dielectric layer is depositedon the first primer layer at a thickness from 600 Å to 800 Å, forexample, from 650 Å to 750 Å or from 675 Å to 725 Å. A second silverlayer is deposited on the second dielectric layer at a thickness from 50Å to 175 Å, for example, from 60 Å to 125 Å, or from 67 Å to 90 Å. Asecond titanium primer layer is deposited on the second dielectric layerat a thickness from 10 Å to 30 Å, for example, from 12 Å to 25 Å, orfrom 15 Å to 22 Å. A third zinc stannate dielectric layer is depositedon the second primer layer at a thickness from 290 Å to 490 Å, forexample, from 340 Å to 440 Å, or 375 Å to 425 Å. A barrier layercomprised of a mixture, alloy, or combination of alumina and silicahaving 60 weight percent alumina to 40 weight percent silicon isdeposited on the third dielectric layer at a thickness ranging from 100Å to 600 Å, for example, from 150 Å to 500 Å, or from 175 Å to 400 Å. Alayer of titania having a thickness ranging from 100 Å to 600 Å, forexample, from 150 Å to 500 Å, or from 175 Å to 400 Å is deposited overthe alumina/silica layer to provide additional durability to thecoating.

Coated substrates according to the present invention can be used forvarious applications such as but not limited to, automotivetransparencies, automotive sidelights, windshields, backlights, sun ormoon roofs, and insulated glass units for residential or commercialwindows, oven doors for gas, electric and microwave ovens.

A substrate coated with the coating according to the present inventiondemonstrates superior performance over conventionally coated substrates.For example, a coated substrate according to the invention willgenerally have better performance in terms of electrical resistivity,haze, solar IR reflectance, visible light transmission, etc. after it isheated during product manufacturing, specifically the type of heatingassociated with bending a piece of glass to produce an automotivewindshield or tempering a glass sheet, because the degradable layer(s)remain in tact. Also, when a layer of barrier coating is the lastcoating layer in a coating stack, a coated substrate according to thepresent invention is better able to withstand mechanical and/or chemicalattack during handling, transport, and storage. Further, the coatingstack has better mechanical durability, chemical durability and heatstability during use such as in a microwave oven door.

The present invention also encompasses a method for creating an enclosedsystem within a multi-layer coating by incorporating at least one layerof barrier coating in a coating stack. The barrier layer can beincorporated anywhere in the coating stack, i.e., within individuallayers of the unit metal based coating stack and/or between unit metalbased coating stacks. The enclosed system refers to the region betweentwo layers of barrier coating or between a layer of barrier coating andthe substrate. Within the enclosed system, essentially no material canenter or leave. The material that can flow through the enclosure isdefined in terms of permeability which is described above.

The method of the present invention enables the interactions betweenlayers of coating within a coating stack to be manipulated so that onlythe desired interactions can occur. Other layers of functional coatingor other materials such as O₂ outside of the enclosed system arerestricted from coming in contact and react with layers within theenclosed system.

The method of the present invention is particularly beneficial when acoating stack contains a layer(s) that should not be exposed to certainmaterials. For example, a coating stack might comprise a metallic layer,like silver, that would degrade if it were exposed to oxygen. In suchcase, the method of the invention can be used to create an enclosed,region without ambient O₂ around the metallic layer by applying a layerof barrier coating both under and above the metallic layer or applying alayer of barrier coating above the metallic layer and utilizing thesubstrate before the metallic layer as the other oxygen barrier.

The following example highlights the benefits of the present invention.A substrate is coated with a multilayered coating composition comprisingthree base stacks similar to those described above. The coating stack isformed via MSVD and the entire coating comprises three layers of silver,four layers of dielectric material (the second dielectric layer of thefirst base stack combines with the first dielectric layer of the secondbase stack to form a single dielectric layer, and the second dielectriclayer of the second base stack combines with the first dielectric basestack of the third unit metal based coating stack to form another singledielectric layer), and three layers of primer. The layers of dielectricmaterial sandwich the silver layers. A layer of primer is applied on alayer of silver before a layer of dielectric is applied. The layer ofbarrier coating is applied over the fourth layer of dielectric materialin the coating stack. The layer of barrier coating creates an enclosedregion between the layer of barrier coating and the substrate.Consequently, the only oxygen that has to be accounted for in the designof the coating stack is the oxygen contained within the system when thecoating stack is being formed as a result of, for example, deposition ofa dielectric layer via MSVD in an oxygen environment. External oxygen isirrelevant because the coating stack is an enclosed system.

As a result of the invention, the layers of primer can be the minimumthickness required to protect the layer(s) of degradable material, e.g.silver, during deposition of the overlaying dielectric layer.Furthermore, less primer than currently taught in the art protect thelayer(s) of degradable material, e.g., silver, during any heating stepsthat are required to bend the coated substrate to a desired contour orto temper coated glass because ambient O₂ is restricted in the system.As mentioned above, after heating, excess primer can lead to failure atthe interfaces of individual layers of coating.

It has been found that in the stack configuration, the primer layer canbe as thin as 12 Å. That is half the thickness required for a similarcoating configuration without a layer of barrier coating that must beable to withstand the deposition process and heating conditions requiredfor bending or tempering the substrate.

Because the present invention allows thinner layers of primer to beutilized in the described coating stack, new materials can be used asthe primer. More specifically, previously certain materials couldn't beused because the primer layers had to be so thick that there was a riskthe layers might not fully oxidize and could form an alloy with thesilver upon heating can be used with the present invention. Suchmaterials include, but are not limited to, aluminum, hafnium, andcobalt-chrome alloy.

The present invention will be illustrated by the following non-limitingexamples.

EXAMPLES

FIG. 1 shows a heat study that was conducted in the following manner.Glass substrates were prepared in the following manner: a 3 inches×6inches×0.08 inch piece of clear float glass was coated with the coatingfacing up on a conveyor belt of a production MSVD coater from VonArdenne. Two, 3 inches×3 inches×0.08 inch clear glass sheets were placedon top of the coated glass to cover the coating. The laminate was passedthrough a Lindberg furnace having five zones. Each zone was 10 incheslong. As described from the entrance of the furnace, the first zone wasat a temperature of approximately 1350° F., the second zone was at atemperature of approximately 1130° F., the third zone was at atemperature of approximately 1180° F., the fourth zone was at atemperature of approximately 1205° F., and the fifth zone was at atemperature of approximately 1195° F.

The exemplary coated substrates were run through the furnace at variousspeeds. Upon leaving the furnace, the 3 inches×3 inches glass sheets ontop of the coated glass were removed and a 0.03 inch thick sheet ofpolyvinylbutyral (PVB) was placed over half of the coated glasssubstrate. The PVB was then covered with one of the 3 inches×3inches×0.09 inch glass sheets that was previously removed to form alaminate over one half of the coated glass. The visible lighttransmittance (LTA) of the laminated half of the coated glass sheet wasmeasured using illuminant A.

It should be appreciated that the slower the belt speed, the longer thecoated glass was exposed to oven conditions, and the hotter the coatedsubstrate became. The belt speed is related to heat budget. Morespecifically, the slower the belt speed, the longer a coating will beexposed to high temperatures, and the higher heat budget the coatingwill have to withstand to exhibit good performance.

In the heat study, all of the coatings were applied on a 3 inches×6inches×2.1 mm clear float glass sheet. The designations for theexemplary coated substrates is described below. The coated substratedesignated “3×Ag(500)” was made in the following manner: a first layerof zinc stannate was applied on the substrate at a thickness of 390 Å; afirst layer of silver was applied on the first layer of zinc stannate ata thickness of 75 Å; a first layer of titanium metal was applied on thefirst layer of silver at a thickness of 15 Å; a second layer of zincstannate was applied on the first layer of titanium metal at a thicknessof 690 Å; a second layer of silver was applied on the second layer ofzinc stannate at a thickness of 75 Å; a second layer of titanium metalwas applied on the second layer of silver at a thickness of 15 Å; athird layer of zinc stannate was applied on the second layer of titaniummetal at a thickness of 690 Å; a third layer of silver was applied onthe third layer of zinc stannate at a thickness of 75 Å; a third layerof titanium metal was applied on the third layer of silver at athickness of 15 Å; a fourth layer of zinc stannate was applied on thethird layer of titanium at a thickness of 390 Å; and a layer of barriercoating comprised of an alloy of alumina and silica sputtered from atarget comprising 60 weight percent aluminum and 40 weight percentsilicon was applied on the fourth layer of dielectric material at athickness of 500 Å.

The coated substrate designated “3×Ag(metal)” was made in the followingmanner: a first layer of zinc stannate was applied on the substrate at athickness of 390 Å; a first layer of silver was applied on the firstlayer of zinc stannate at a thickness of 75 Å; a first layer of titaniummetal was applied on the first layer of silver at a thickness of 15 Å; asecond layer of zinc stannate was applied on the first layer of titaniummetal at a thickness of 690 Å; a second layer of silver was applied onthe second layer of zinc stannate at a thickness of 75 Å; a second layerof titanium metal was applied on the second layer of silver at athickness of 15 Å; a third layer of zinc stannate was applied on thesecond layer of titanium metal at a thickness of 690 Å; a third layer ofsilver was applied on the third layer of zinc stannate at a thickness of75 Å; a third layer of titanium metal was applied on the third layer ofsilver at a thickness of 15 Å; a fourth layer of zinc stannate wasapplied on the third layer of titanium metal having a thickness of 100Å; and a layer of titanium metal was applied on the fourth layer of zincstannate at a thickness of 26 Å.

The coated substrate designated “2×Ag(500)” was made in the followingmanner: a first layer of zinc stannate was applied on the substrate at athickness of 390 Å; a first layer of silver was applied the first layerof zinc stannate at a thickness of 75 Å; a first layer of titanium metalwas applied on the first layer of silver at a thickness of 15 Å; asecond layer of zinc stannate was applied on the first layer of titaniummetal at a thickness of 690 Å; a second layer of silver was applied onthe second layer of zinc stannate at a thickness of 75 Å; a second layerof titanium metal was applied on the second layer of silver at athickness of 15 Å; a third layer of zinc stannate was applied on thesecond layer of titanium metal at a thickness of 390 Å; and a layer ofbarrier coating comprised an alloy of alumina and silica sputtered froma target comprising 60 weight percent aluminum and 40 weight percentsilicon was applied on the third layer of zinc stannate at a thicknessof 500 Å.

A commercial sample is included in FIG. 1. In this sample, a glasssubstrate was coated with Sungate® Automotive Coating Number 5 (“SA05”)which is commercially available from PPG Industries in Pittsburgh, Pa.SA05 is a double silver layer, heatable coating.

CONCLUSION

As shown in the heat study of FIG. 1, the barrier coating of the presentinvention protects the degradable layer(s) and thereby maintains theperformance of the coating. Coated substrates having a 500 Å layer ofbarrier coating according to the present invention—“3×Ag(500)” and“2×Ag(500)”—maintained a fairly constant LTA regardless of the beltspeed. The example identified as 3×Ag(500) showed a drop in LTA from 77%to 74% as the belt speed dropped from 9 ipm to 3 ipm. The exampleidentified as 2×Ag(500) showed a drop in LTA from 76% to 72% as the beltspeed dropped from 9 ipm to 3 ipm. Because “3×Ag(500)” and “2×Ag(500)”contain primers layers at a thickness of 15 Å, the reduction in LTA dueto a reduction in belt speed is much less than expected.

Substrates that did not have a layer of barrier coating according to thepresent invention showed more severe drop-offs in regards to LTA withslower belt speeds than substrates coated according to the presentinvention. The example identified as 3×Ag(metal) showed a drop in LTAfrom 75% to 62% as the belt speed dropped from 9 ipm to 3 ipm. Theresults show titanium does not have as good barrier properties as thelayer of barrier coating described in the present invention. Thecommercial sample showed a drop in LTA from 72% to 61% as the belt speeddropped from 9 ipm to 5 ipm and then the LTA increased from 61% to 64%as the belt speed dropped from 5 ipm to 3 ipm.

It will be readily appreciated by those skilled in the art thatmodifications can be made to the invention without departing from theconcepts disclosed in the foregoing description. Such modifications areto be considered as included within the scope of the invention.Accordingly, the particular embodiments described in detail hereinaboveare illustrative only and are not limiting as to the scope of theinvention, which is to be given the full breadth of the appended claimsand any and all equivalents thereof.

What is claimed is:
 1. A method of forming a multilayered coatedsubstrate, comprising: providing a substrate; applying a first barrierlayer over at least a portion of a substrate, wherein the first barrierlayer has a permeability to oxygen of no greater than 10 grams per m²per day at a temperature of 900° F., and wherein the first barrier layercomprises a mixture of silica and alumina having greater than or equalto 40 wt. % silica; applying a first dielectric layer over the firstbarrier layer; applying at least one degradable metal layer over thefirst dielectric layer; applying a primer layer over the at least onedegradable metal layer; applying a second dielectric layer over theprimer layer; and applying a second barrier layer over the seconddielectric layer, wherein the second barrier layer has a permeability tooxygen of no greater than 10 grams per m² per day at a temperature of900° F., and wherein the barrier layer comprises a mixture of silica andalumina having greater than or equal to 40 wt. % silica; and passing themultilayered coated substrate through a furnace having a line speed from9 inches per minute (“ipm”) to 5 ipm, the resulting multilayered coatedsubstrate has a visible light transmittance of at least 70 percent. 2.The method according to claim 1, wherein the first barrier layer or thesecond barrier layer has a thickness from 50 Å to 5,400 Å.
 3. The methodaccording to claim 1, wherein the applying the first barrier layer orthe applying the second barrier layer step comprises depositing thefirst barrier layer or the second barrier layer by a magnetron sputteredvacuum deposition (“MSVD”) technique using a target comprising about 60weight percent aluminum and 40 weight percent silicon.
 4. The methodaccording to claim 1, wherein the primer has a thickness in the rangefrom 10 Å to 18 Å.
 5. The method according to claim 1, wherein thepermeability to oxygen for the first barrier layer or the second barrierlayer is no greater than 5 g/m²/day.
 6. The method according to claim 1,wherein the permeability to oxygen for the first barrier layer or thesecond barrier layer is no greater than 0.6 g/m²/day.
 7. The methodaccording to claim 4, wherein the primer is selected from the groupconsisting of titanium, aluminum, hafnium and a cobalt-chrome alloy. 8.The method according to claim 4, wherein the primer is titanium.
 9. Themethod according to claim 8, wherein the primer has a thickness between12 Å and 15 Å.
 10. A method of forming a multilayered coated substrate,comprising: forming a coating over a substrate, the coating comprising aradiation reflective metal layer over the substrate, a primer layerdirectly on the radiation reflective metal layer, and a first barrierlayer over the primer layer; wherein the barrier layer has apermeability to oxygen of no greater than 10 grams per m² per day at atemperature of 900° F., and wherein the barrier layer comprises amixture of silica and alumina having greater than or equal to 40 wt. %silica; and passing the coated substrate through a furnace having a linespeed from 9 ipm to 5 ipm, wherein the resulting multilayered coatedsubstrate has a visible light transmittance of at least 70 percent. 11.The method according to claim 10, wherein the second barrier layer isthe outermost layer of the coating.
 12. The method according to claim10, wherein the first barrier layer is the outermost layer of thecoating.
 13. The method according to claim 10, wherein the first barrierlayer comprises about 60 weight percent alumina and about 40 weightpercent silica.
 14. The method according to claim 10, wherein the primerhas a thickness in the range from 10 Å to 18 Å.
 15. The method accordingto claim 10, wherein the permeability to oxygen for the first barrierlayer is no greater than 5 g/m²/day.
 16. The method according to claim10, wherein the permeability to oxygen for the first barrier layer is nogreater than 0.6 g/m²/day.
 17. The method according to claim 14, whereinthe primer is selected from the group consisting of titanium, aluminum,hafnium and a cobalt-chrome alloy.
 18. The method according to claim 14,wherein the primer is titanium.
 19. The method according to claim 18,wherein the primer has a thickness between 12 Å and 15 Å.
 20. The methodaccording to claim 11 further comprising providing a second barrierlayer between the coating and the substrate, wherein the barrier layerhas a permeability to oxygen of no greater than 10 grams per m² per dayat a temperature of 900° F., and wherein the barrier layer comprises amixture of silica and alumina having greater than or equal to 40 wt. %silica.
 21. A method of forming a multilayered coated substrate,comprising: applying a first layer on a substrate; applying a firstmetal layer over the first layer; applying a first primer layer over thefirst metal layer; applying a second layer over the first primer layer;applying a second metal layer over the second layer; applying a secondprimer layer over the second metal layer; applying a third layer overthe second metal layer; applying a barrier coating over the third layer;wherein the barrier layer has a permeability to oxygen of no greaterthan 10 grams per m² per day at a temperature of 900° F., and whereinthe barrier layer comprises a mixture of silica and alumina havinggreater than or equal to 40 wt. % silica; and passing the multilayeredcoated substrate through a furnace having a line speed from 9 ipm to 5ipm, the resulting multilayered coated substrate has a visible lighttransmittance of at least 70 percent.
 22. The method according to claim21, wherein the first layer, the second layer or the third layercomprises zinc stannate.
 23. The method according to claim 21, whereinthe first metal layer or the second metal layer comprises silver. 24.The method according to claim 21, wherein the first primer layer or thesecond primer layer comprises titanium.